The present invention relates generally to water filter cartridges used in home and business water filter systems, and optionally used in commercial applications. Current filter systems have a manifold head with a manifold head inlet port connected to a source of water and a manifold head outlet port connected to a dispenser for the filtered water, such as a household refrigerator, or an apparatus using filtered water such as a coffee maker. The manifold head typically has a generally cylindrical, cup shaped interior, and often has a single, uniform diameter or two different diameters forming a stepped configuration. A removable filter cartridge has a cartridge head that is typically inserted axially into the manifold head so that lugs or bayonet flanges on the cartridge head or cartridge housing pass through corresponding slots in the manifold head. The cartridge is then rotated so the lugs or bayonet flanges engage inclined locking surfaces on the manifold head to force the cartridge and cartridge head axially toward the manifold head so as to engage fluid seals located between the manifold head and the cartridge head and to align the manifold head inlet port with a cartridge head inlet and to align a cartridge head outlet with the manifold head outlet port so water can flow through a filter within the cartridge. The cartridge head is rotated the opposite direction to remove the cartridge after the filter is exhausted and to allow a fresh filter cartridge to be inserted into the manifold head.
Two or three O-ring seals are used between the manifold head and the cartridge head to separate the inlet and outlet flow paths to and from the filter cartridge. One of the seals allows water to flow between the interior end of the manifold head and the adjacent end of the cartridge head in a plane orthogonal to the longitudinal axis of the filter cartridge, or the seals allow water to flow between an annular surface on the manifold head and an adjacent annular surface on the cartridge head, which annular surfaces encircle the longitudinal axis of the filter cartridge. The water pressure on these adjacent and opposing manifold head and cartridge surfaces that are orthogonal to or inclined relative to the longitudinal axis of the filter cartridge exert an axial force on the cartridge that is proportional to the surface area and water pressure. This axial force urges the cartridge out of the manifold head and is resisted by the cartridge lugs engaging the locking surfaces on the manifold head.
The lugs on the cartridge head or cartridge and the mating locking surfaces on the manifold head are substantial in order to maintain the cartridge firmly engaged with the manifold head. The line pressure of a municipal water source is typically about 40-60 psi and the manifold head and/or cartridge head is constructed so that the water exerts an axial pressure that pushes the cartridge head and cartridge away from the manifold head. The larger the diameter of the filter cartridge and cartridge head, the larger the axial force pushing the filter cartridge away from the manifold head and the larger the axial force that must be restrained by the lugs and locking surfaces. Since the filter cartridges are disposable the cartridge heads are of molded plastics, requiring the lugs to be about ¼ to ⅜ inch thick in the axial direction of the filter cartridge in order to secure the cartridges into position in the manifold head with each lug extending about an inch or more around a circumference of the cartridge's cartridge head, and with the manifold head locking surfaces having a similar thickness and circumferential length. These substantial lugs and locking surfaces require extensive molding and material. There is thus a need for an improved engagement mechanism that reduces the size of the mating lugs and locking surfaces.
The lugs and locking surfaces are thicker in the axial direction to accommodate the increased forces and since the length of the manifold head and cartridge are limited, the result is that the size of and length of the mating head is larger and the thickness of the lugs is larger in order to accommodate the increased axial force from the line water pressure tending to push the filter cartridge out of the mating head. Further, not only must the lugs on the filter cartridge be larger to accommodate the axial force from the line pressure but the mating surfaces on the head must also be larger to accommodate the force and to accommodate the larger filter lugs. Basically, the lugs on the filter cartridge and the mating lugs or locking surfaces on the manifold head must be similar in size in order for them to work together. There is thus a need for cartridge connecting and retaining mechanism that better accommodates the line pressure of the water source.
Additionally, the flow rate through the filter cartridges also increases the potential axial force tending to eject the filter from the manifold head or head. Historically a ¾ opening was considered large whereas current openings about 1″ in diameter may be considered a minimum in some instances and 1½″ and 2″ diameter flow openings in the filter cartridges are becoming more common. With the increased flow rate the potential axial ejection force increases. There is thus a need for a water filter cartridge connecting and retaining mechanism that does not require so much axial length. There is thus a need for a water filter cartridge that better accommodates the increasing flow rates and resulting potential for increased forces tending to eject the filter from the manifold head.
The axial force resisted by the lugs ultimately limits the diameter of usable filters to about five inches diameter. There is thus a need for a way to removably connect replaceable filter cartridges to manifold heads that more efficiently accommodates the force created by the line pressure of the water source.
As the lugs and locking surfaces become longer in the axial and circumferential directions, it takes more force to rotate the filter cartridge about the longitudinal axis of the cartridge to engage the lugs and locking surfaces in the circumferential direction and to move the cartridge axially into position within the manifold head. This increased rotational torque presents difficulties for those with weaker arm strength, especially as the cartridge locations may be difficult to access. There is thus a need for an improved way to releasably engage the removable filter cartridge with the manifold head.
As water pressure is initially applied to an inserted cartridge, the O-ring seals between the cartridge and manifold head will move slightly before they seat and seal, and that typically allows a small amount of water to leak past the seal. Rapid changes in the line pressure can cause similar movement of the seals and slight leakage or weeping of water past the seals and into the dead spaces. The pressure spikes become more problematic if an O-ring forms part of two different flow paths so that an unequal pressure is exerted on different O-rings. The result is that small amounts of unfiltered water can bypass the filter element completely and allow unfiltered water into the filtered water side thereby contaminating the filter. A very low pressure or no-pressure application may also result in O-rings seals that are not seated sufficiently to prevent small amounts of water passing the seals. The result is that Bacteria and other undesirable growths can develop and ultimately bypass the seals, passing from the filtered water side to the non-filtered side, or passing from the non-filtered side to the filtered side. For many applications this bypass and actual or potential contamination is undesirable, but tolerated. For some applications this bypass and actual or potential contamination is unacceptable, as in pharmaceutical or biological applications where contamination of the filtered water may cause contamination or quality control problems and in such situations the solid seals may be used, such as adhesives, to avoid even small leaks. There is a need to avoid these small leaks that occur with pressure spikes or from no pressure or so low a pressure as to adequately seat the seals.
Additionally, current contamination testing techniques allow the identification of chemical contamination down to the parts per trillion levels. Thus, even very small amounts of water bypassing the O-ring from the non-filtered side to the filtered side of the cartridge may show up. While a water filter cartridge may pass a specific contamination test when operating in a steady flow condition that same filter cartridge may fail that same test when water pressures rise and fall dramatically between the inlet and outlet—particularly with membrane or other filter media that have high pressure drop across them. There is thus a need for an improved seal between inlet and outlet flow paths of a water filter cartridge.
Once a water filter cartridge is installed, users assume the cartridge will not leak. Unfortunately, sometimes the cartridge is installed improperly or for other reasons does not seal properly internally during manufacturing and the cartridge does leak and/or the filter media is bypassed. If the leak is readily identifiable it may be checked at the time of installation. Unfortunately, most filter cartridges do not allow easy inspection to see if the cartridge is leaking. One exception is U.S. Pat. No. 8,216,463, which provides a seal that allows leak inspection. But that leak detection is not suitable for all applications. There is thus a need for an improved method and apparatus to indicate whether a removable filter cartridge is leaking, and/or bypassing especially at the time of installation when the cartridge may be readily examined, reinstalled or replaced if needed.